A FTTH network is an optical access network providing a number of end users with communication services, e.g. with services requiring data transmission at a rate of some hundreds of Mbit/s or more.
Typically, a FTTH network comprises a distribution cabinet cooperating with a transport network. The distribution cabinet is often located in the basement of the building where the end users reside and is connected with termination boxes arranged, for example, at the various building floors via optical cables, housing one or more optical fibers.
An optical cable comprising a plurality of optical fibers typically exits the distribution cabinet. In the following of the present description, an optical cable which exits a distribution cabinet and serves each floor of a given building to reach each end user will be indicated as “in-line optical cable”. Further, in the following of the present description, each optical fiber of an in-line optical cable will be indicated as “in-line optical fiber”.
Typically, the in-line optical cable vertically runs through the building from the basement up to all the building floors. The in-line optical cable is typically laid down within a duct, which is substantially vertically fixed to a building wall and which mechanically protects the in-line optical cable.
In the following of the present description, the duct which receives an in-line optical cable will be indicated as “in-line cable duct”.
Typically, an optical cable comprising comprises one or more optical fibers, generally two, branches out the in-line optical cable and exit the termination box for connecting the end user at a certain floor. In the following of the present description, said optical cable branching out the in-line optical cable will be indicated as “drop cable”. Further, in the following of the present description, each optical fiber of a drop cable will be indicated as “drop optical fiber”.
Connecting the distribution cabinet to a termination box requires extracting at least one in-line optical fiber from the in-line optical cable and connecting, typically by splicing, such an in-line optical fiber to a drop optical fiber of said drop cable exiting the termination box. The optical connection between the in-line optical cable and the drop cable is typically made in a so-called “optical transition box”.
An optical transition box typically comprises a base and a cover. The base has a bottom and, typically, four sidewalls. One of the sidewalls has a number of holes (usually up to 12 holes) each shaped for allowing the free end of a respective drop cable to be inserted into the optical transition box. Typically, the base of the optical transition box is provided with a plurality of tracks for properly arranging the optical fibers therein. Generally, each track is provided with straight portions and curved portions, each curved portion having a bending radius of at least 20 mm in order to minimize the bending losses of the arranged optical fibers. The base of the optical transition box is also provided with an area suitable for housing the joints (i.e. fusion splices and/or mechanical joints) between optical fibers.
Optical transition boxes are typically configured to be associated to the in-line cable duct so that a portion of the in-line cable duct is housed within the box. To this purpose, two opposite sidewalls of the box have respective recesses for housing an in-line cable duct so that a portion of the in-line cable duct is contained in the optical transition box.
Accordingly, installation of an optical transition box firstly requires fixing the bottom of the optical transition box base to a wall of the building so that the recesses of the two opposite sidewalls are substantially vertically aligned. Then, the in-line cable duct is usually vertically oriented and inserted in the recesses so that a portion thereof is contained within the box. The portions of the in-line cable duct entering and exiting the box are fixed to the building wall as well. A window is made in the portion of the in-line cable duct which is contained in the optical transition box so that the in-line cable is exposed and the outer sheath thereof can be peeled off for accessing the in-line optical fibers.
The free end of each drop cable connected to a respective termination box is inserted in a respective hole of a sidewall of the optical transition box base so that a portion of the drop cable is received in the box and the outer sheath of the drop cable can be peeled off for some tens of centimeters (starting from the free end thereof) for allowing the respective drop optical fiber(s) to be exposed.
At least one in-line optical fiber is connected to a respective drop optical fiber by means of fusion splicing or a mechanical joint.
The in-line optical fibers and drop optical fibers are then arranged in the tracks provided in the box base and the splices/mechanical joints are arranged in the dedicated area of the box base.
Finally, the cover is positioned onto the box base so that the optical transition box results to be safely closed.